Investigation of Ag in the king scallop Pecten maximus using field and laboratory approaches

The bioaccumulation, tissue and subcellular distributions of Ag were investigated in the king scallop Pecten maximus from the Bay of Seine fishery area (France) in laboratory and in field conditions. Experimental investigations with the radiotracer ^110mAg showed that the scallop readily concentrated Ag when exposed via seawater and to a much lower extent when exposed via sediment. Retention of the metal incorporated via all tested contamination pathways was shown to be very strong, but the assimilation efficiency of Ag ingested with food was found to be tightly depending on the phytoplankton strain used to feed the scallops (74 and 33% with Skeletonema costatum and Isochrysis galbana, respectively). The uptake and depuration kinetic parameters determined in the laboratory experiments were used to run a global bioaccumulation model. The latter indicated that the major uptake pathway of Ag in P. maximus was strongly depending on the food quality. Indeed, when fed the diatom S. costatum which was characterised by a high affinity for Ag (high distribution constant K_df) the relative contribution of the feeding pathway reached 98% of the global Ag bioaccumulation. In contrast, when fed I. galbana which displayed a lower K_df than S. costatum, dietary Ag was retained to a lesser extent by P. maximus, and seawater appeared as the major contributing uptake pathway. In wild scallops collected from reference and contaminated sites, Ag was mainly concentrated in the digestive gland and secondarily in the gills, and was mainly found associated with the insoluble subcellular fraction in all the scallop tissues.